Microcontact printing (μCP) is a flexible, non-photolithographic method for forming patterned materials, preferably self-assembled monolayers (SAMs) on a substrate surface. Microcontact printing advantageously permits the generation of patterned SAMs having submicron lateral dimensions.
Microcontact printing has found application in microfabrication processes, such as the manufacture of microelectronic devices, integrated circuits, and computer chips. The capability of microcontact printing to transfer SAM-forming molecular species to a substrate has also found application in patterned electroless deposition of metals and the patterning of proteins on a substrate for improved biological assay techniques. Kind, H., et al., Langmuir, 16:6367-73 (Aug. 8, 2000); Bernard, A., et al., Langmuir, 14:2226-28 (Apr. 28, 1998) (incorporated herein by reference).
Microelectronic devices have long been prepared by the methods of photolithography. According to this technique, a thin film of conducting, insulating, or semiconducting material is deposited on a substrate and a negative or positive photoresist is coated onto the exposed surface of the material. The resist is then irradiated in a predetermined pattern, and irradiated or non-irradiated portions of the resist are washed from the surface to produce a predetermined pattern of resist on the surface. Photolithography, however, provides limited resolution due to optical diffraction limitations. As a result, increasingly smaller microfabricated structures are too difficult, or too expensive, to manufacture commercially.
Microcontact printing promises a significant advance over conventional photolithographic techniques because of the increased resolution enabled by microcontact printing. Microcontact printing is characterized by extremely high resolution enabling patterns of submicron dimension to be imparted onto a substrate surface. Microcontact printing is also more economical than photolithography systems since it is procedurally less complex and can be carried out under ambient conditions. In addition, microcontact printing permits higher throughput production than other techniques, such as e-beam lithography (a conventional technique employed where higher resolutions are desirable).
Microcontact printing is also more amenable to a wider variety of surfaces that make photolithography an impractical option. For example, microcontact printing may be used on cylindrical or spherical surfaces, or discontinuous or multiplanar surfaces. Because photolithography is a projection technique, a comparatively smaller depth of field prevents its use over non-planar surfaces. Further, photolithography does not permit the patterning of biomaterials, whereas microcontact printing may.
Microcontact printing is not limited by the optical boundaries of photolithography. The principles of microcontact printing are disclosed, for example, in U.S. Pat. No. 5,512,131, incorporated herein by reference. Background information on microcontact printing is also disclosed in Xia, Y. and Whitesides, G. M., “Soft Lithography”, Angew. Chem. Int. Ed., 37: 550-575 (1998), incorporated herein by reference. SAMs are generally prepared by exposing a surface to a solution containing a ligand that is reactive towards the surface. A well characterized SAM system is alkanethiolate CH3(CH2)nS− on gold. In this exemplary SAM, alkanethiols chemisorb spontaneously on the gold surface from solution and form adsorbed alkanethiolates. Sulfur atoms bonded to the gold surface bring the alkyl chains into close contact, leading to an ordered structure. Alkanethiolates with n>11 form the closely packed and essentially 2-dimensional organic quasi-crystals supported on gold that characterize the SAMs thus far shown to be most useful in microcontact printing.
Until the present invention, microcontact printing has been carried out entirely, or in part, by hand. The steps necessary to perform microcontact printing using previous methods were difficult, time consuming, and inefficient, making the process less valuable commercially. The few partially automated processes applied to microcontact printing have controlled few parameters (particularly where alignment is concerned), thus restricting the printing process' adaptability to commercial demands. Automated, controlled microcontact printing promises greater control (and hence optimization) of process variables, which in turn promotes higher quality printing and higher throughput. Moreover, the previous methods of performing microcontact printing were dependent on the skill of the operator, leading to variation in the final product. Thus, a need exists for substantially automating the entire process of microcontact printing.
The present invention provides a method of reproducibly and conveniently producing a printed pattern (e.g., a SAM pattern, or variety of SAM patterns), on planar or non-planar surfaces, the method providing patterns having resolutions extending into the submicron range and the process being fully automated and controlled to meet commercial applications.